Question: Tell me about castle for commissioned by of William the Conqueror?
SPARQL (Wikidata):  select distinct ?sbj where { ?sbj wdt:P88 wd:Q37594 . ?sbj wdt:P31 wd:Q23413 } 
Answer: Colchester Castle, Cardiff Castle, Pevensey Castle, Bristol Castle, Rougemont Castle, Wisbech Castle, Windsor Castle, Tower of London